In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA) system, Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few.
3GPP Long Term Evolution (LTE) is a project within the 3rd Generation Partnership Project (3GPP) to evolve the WCDMA standard towards the fourth generation of mobile telecommunication networks. In comparisons with WCDMA, LTE provides increased capacity, much higher data peak rates and significantly improved latency numbers. For example, the LTE specifications support downlink data peak rates up to 300 Mbps, uplink data peak rates of up to 75 Mbps and radio access network round-trip times of less than 10 ms. In addition, LTE supports scalable carrier bandwidths from 20 MHz down to 1.4 MHz and supports both Frequency Division Duplex (FDD) and Time Division Duplex (TDD).
Furthermore, the latest release, also referred to as release 10, of LTE is 3GPP's candidate for International Mobile Telecommunications—Advanced (IMT-A) technology which is expected to provide among other things, peak rates as high as 1 Gbps in downlink (DL), and several hundreds of Mbps in uplink (UL). One of the major additions to LTE Release 10 from the initial LTE release, i.e. release 8, is the concept of relaying.
In all simplicity, the concept of relaying consists of deploying a radio network node, also referred to as a Relay Node (RN), in a cell of the radio communications network in order to provide radio coverage in black spots in the cell or beyond the cell and also possibly increase the capacity in already radio covered spots. The relaying concept may comprise only one relay node in the cell but is more likely to comprise multiple relay nodes per cell. Thus, the relay node forwards data in the uplink to a radio base station or to a different relay node, or forwards data to a user equipment or to a different relay node in the downlink.
The connection between the radio base station and the relay node is referred to as the backhaul link over an air interface denoted as Un. It is on the backhaul link that communication between radio base station and relay node takes place. The connection with the user equipment within the cell, whether from the radio base station or the relay node, is known as the access link over an air interface denoted as Uu.
In order to coordinate transmissions, Un and Uu share the frequency bandwidth, whether in uplink or in downlink by strict time division multiplexing (TDM). Strict TDM means that in case a Un link is configured, the relay node cannot have any Uu links configured. Based on a configuration of a certain slot, i.e. whether backhaul link or access link, and based whether it is an UL or DL phase, some nodes will transmit whereas others will listen.
Using multiple relay nodes in a cell enhances the performance of the user equipments traditionally having low Signal to Interference plus Noise Ratios (SINR) in the radio communications network. However, such gains of performance have been curbed by some major limitations in the achievable high rates in LTE release 10. It has been detected that mainly cell edge users and user equipments having bad radio conditions gain from the concept of relaying. Although relaying is able to enhance the performance of user equipments in bad radio conditions, it creates a problem for user equipments with already high SINR, leading to limiting the peak rates by e.g. 50% when the resource allocation is divided equal between the access link and the backhaul link.